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Pentax 120mm f/4 Macro
(Discontinued about 2000)
© 2009 KenRockwell.com. All rights reserved.

Intro   Specs   Performance   Usage   Recommendations

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Pentax 645 120mm Macro

SMC Pentax-A 120mm f/4 Macro. enlarge. You can find these used at these direct product links to Adorama and eBay. It helps me keep adding reviews of this old stuff when you use these links to get yours, Thanks! Ken.


January 2009        more Pentax reviews


Introduction          top

Intro   Specs   Performance   Usage   Recommendations

This is Pentax' manual focus macro lens for the Pentax 645, 645N and 645NII medium-format cameras. It is wonderful because it focuses all the way up to 1:1 life size in one turn of the big focus ring.

It works in all the automatic and manual exposure modes of the Pentax 645, 645N and 645NII.

These lenses are bargains today. I paid $200 through eBay in December 2008, and dealers ask about $350. Back in December 1997, B&H got $760 for this lens new. That's over $1,000 in 2009 with inflation.

This manual-focus macro lens was replaced by the autofocus version in about 2001, which then sold for $1,150.

Unlike Nikon, with Pentax 645, you lose nothing except AF with this manual lens on the autofocus Pentax 645 cameras. With the AF 645 cameras (645N and 645N II) you even get full film-edge data imprinting!

Pentax 645 120 4 Macro

Pentax 645 120/4 Macro. enlarge.


Specifications      top

Intro   Specs   Performance   Usage   Recommendations



9 elements in 7 groups.

Floating elements to adjust the optics for peak performance at every distance.



Focal Length


35mm equivalent: It sees an angle of view on 645 film similar to what a 75mm lens sees on 35mm film.

See also my 35mm Equivalent Focal Length Chart for other 645 lenses.



8 blades stopping down to f/32.

Arbitrary half and full-stop clicks.


Close Focus

1.3 feet (0.39m).


Maximum Reproduction Ratio

1:1 (life-size).


Filter Thread


Does not rotate with focus.



3.09" diameter x 4.33" long (78.5 x 110mm).



24.520 oz. (695.2g) measured naked.

31.078 oz. (881.0g) measured with caps and case.

Pentax specifies 24.5 oz. (695g).



Pentax suggests the A645 2X and 1.4x converters.

Pentax 645 120mm f/4 Macro

Pentax 645 120 4. enlarge.


Performance        top

Intro   Specs   Performance   Usage   Recommendations

The Pentax 645 120mm macro just works. It's not the sharpest at infinity in the corners wide-open, but that's not why you buy a macro lens.

It does everything else so well and it feels so good in-hand that it's hard to fault.



Bokeh is perfectly neutral.



The Pentax 120mm f/4 has no visible distortion.

For very critical use, plug +0.5 into Photoshop CS2's lens distortion filter to correct the invisible barrel distortion when used at 10 feet (3 meters). I haven't measured it for other distances.



I love it!

The focus ring feels fantastic. It's much slipperier and smoother than you'd expect. It's easy to focus both fast and precisely.



There is little to no light falloff in the corners.

There's a tiny amount at f/4, only visible if you're comparing by flipping between the same image made at smaller apertures.

Any falloff is gone by f/5.6.



There's no problem using any any 67mm filter. There should be no problem stacking them, either.



This is one of the best parts: focus is a dream.

I can focus with just one finger, and with two I can flick it from near to far.

It's slick, smooth and perfect.

Not only is it smooth and slick, it doesn't have any focus creep. I have other manual focus lenses from Nikon which will creep if pointed up or down, but this Pentax stays where it's put even without a lock.


Mechanics and Construction

The Pentax 645 120mm is made as it should be.

Barrel: Enameled, anodized aluminum.

Focus Ring: Metal, rubber covered.

Aperture Ring: Metal.

Depth-of-Field Scale: Yes, but only for f/32.

Infra-Red Focus Index: No.

Finish: Black enamel over black anodize.

Mount: Metal with some plastic nubbins.

Internals: Metal.

Markings: Engraved and filled with paint.



It's softer in the corners at f/4 and infinity, and gets sharper stopped down.

Oddly, even with floating elements, this isn't as good as the Pentax 645 150mm f/3.5 at infinity, which is perfectly sharp even at f/3.5 wide open.

This 120mm is sharp wide-open close up, too, even at 1:1 shooting hand-held.

Cased Pentax 120mm

Pentax 645 and its case. enlarge.


Usage       top

Intro   Specs   Performance   Usage   Recommendations

It's easy to focus: the ring turns with uncanny smoothness and a minimum of drag.

Far better than Canon and Nikon macro lenses, the reproduction ratios are marked on a separate scale on the front of the focus ring, near the front of the 120mm macro lens.

In the example below, it's set to a 1:5 reproduction ratio. This means the image on film is 1/5 the size of the subject:

Pentax 120mm Macro Repro scale

Reproduction Ratio Scale (at top), set to 1:5. enlarge.


And here it is set to 1:1:

Pentax 120/4 Erect

Pentax 645 120mm Macro at 1:1. enlarge.


Recommendations       top

Intro   Specs   Performance   Usage   Recommendations

For ordinary tele use, I'd use the Pentax 645 150mm f/3.5 instead because it's sharper wide open at normal distances, it's smaller, lighter, has a built-in hood and is half the price.

For macro in the Pentax 645 system, your choices in 2009 are either this lens or the Pentax 645 AF Macro. I've never used the AF version of this lens.

I shoot all my macro in manual focus anyway, so I wouldn't bother holding out for the AF 120mm f/4. I use this one and love it.

What I can't convey here is just how good it feels. When you pick one up and focus it you'll know what I mean. It feels so good you just want to hold and focus it, even if you're not shooting.



I support my growing family through this website.

If you find this as helpful as a book you might have had to buy or a workshop you may have had to take, feel free to help me continue helping everyone.

If you've gotten your gear through one of my links or helped otherwise, you're family. It's great people like you who allow me to keep adding to this site full-time. Thanks!

If you haven't helped yet, please do, and consider helping me with a gift of $5.00.

The biggest help is to use these links to Adorama, Amazon, B&H, Calumet, Ritz, J&R and when you get your goodies. It costs you nothing and is a huge help to me. eBay is always a gamble, but all the other places have the best prices and service, which is why I've used them since before this website existed. I recommend them all personally.

Thanks for reading!


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